Reverse Conductive Switches in Modular Converter Submodules
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Solution Overview
Problem
Existing modular multi-level converters experience high operating losses due to the use of non-reverse conductive power semiconductor switches, which are also expensive, and there is a need for a cost-effective solution that reduces these losses.
Innovation Solution
The solution involves using reverse conductive power semiconductor switches only in the bridging branch between the connection terminals, where they are subjected to higher loads, and non-reverse conductive switches with freewheeling diodes at less heavily loaded points, optimizing the reverse conductive switches for low forward voltage and the non-reverse conductive switches for low storage charge to minimize losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If reverse conductive power semiconductor switches are used in all positions, then operating losses are reduced, but device cost increases
Solution Approach 1:
The patent applies reverse conductive power semiconductor switches only in the bridging branch where they are most needed for loss reduction, while using conventional switches with freewheeling diodes in other positions. This localized application of the expensive component optimizes the trade-off between operating losses and device cost.
Solution Approach 2:
The converter bridge is segmented into different functional zones: the bridging branch uses reverse conductive switches for optimal performance, while other branches use conventional switches. This segmentation allows selective application of the expensive technology only where it provides the most benefit.
2Loss of energy
If reverse conductive power semiconductor switches are used, then forward voltage drop is reduced, but component cost increases
Solution Approach 1:
Reverse conductive switches with lower forward voltage drop are installed only in the bridging branch where voltage reduction provides maximum loss reduction benefit, rather than uniformly across all switch positions. This local optimization balances performance improvement with cost considerations.
3Ease of manufacture
If non-reverse conductive switches with freewheeling diodes are used, then device cost is reduced, but operating losses increase
Solution Approach 1:
Conventional switches with freewheeling diodes are used in positions where they provide adequate performance at lower cost, specifically outside the bridging branch. This allows cost reduction in less critical positions while maintaining overall system efficiency.
Data Source
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AI summary
In order to provide a submodule (13) for a modular multilevel converter (1) comprising at least one unipolar energy store (14), a first and a second connection terminal (16, 17) and a power semiconductor circuit comprising power semiconductor switches (T1, T4, 19) that can be turned on and off by means of a control signal and freewheeling diodes (D1, D2) connected in parallel with an assigned power semiconductor switch (T1,T4) in the opposite sense, wherein, depending on the driving of the power semiconductor switches (T1, T4, 19), the voltage dropped across one or all of the energy stores (14) or else a zero voltage can be generated between the first and the second connection terminals (16,17), and wherein the power semiconductor circuit forms a bridging branch (18) situated between the potential points of the first and second connection terminals (16, 17), which submodule has low on-state losses during normal operation and, moreover, is also cost-effective, it is proposed that only the power semiconductor switches arranged in the bridging branch (18) are reverse conductive power semiconductor switches (19).